Fe-Cr-Co-Ni-Al eutectic high-entropy alloy and preparation method thereof

Abstract

The invention relates to the technical field of high-entropy alloys, in particular to a Fe-Cr-Co-Ni-Al eutectic high-entropy alloy and a preparation method thereof. And for the FeaCrbCocNidAle eutectic high-entropy alloy with a = 1, b = 1, c = 1, d = 2.1 and e = 1, the mechanical property of the FeaCrbCocNidAle eutectic high-entropy alloy needs to be further improved so as to meet the requirement of strong plasticity matching. In order to solve the technical problems, the Fe-Cr-Co-Ni-Al eutectic high-entropy alloy is provided, the chemical components of the alloy are designed and expressed as FeaCrbCocNidAle according to the atomic ratio, a is 49, b is larger than or equal to 25 and smaller than or equal to 30, c is 9.8, d is larger than or equal to 5 and smaller than or equal to 15, e is 2, a + b + c + d + e is 100, Fe49Cr28.4 Co9.8 Ni10.8 Al2 is the eutectic high-entropy alloy, the yield strength is 612 MPa, the tensile strength is 823 MPa, the elongation at break is 25.1%, and the strength and plasticity matching is good. The problem that an existing high-entropy alloy is poor in strength and plasticity matching is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-entropy alloys, and particularly relates to a Fe-Cr-Co-Ni-Al eutectic high-entropy alloy and a preparation method thereof. Background Art

[0002] High Entropy Alloys (HEAs) have attracted much attention due to their unique multi-component solid solution structure and excellent comprehensive properties. HEAs are generally composed of five or more main elements, and the proportion of each main element is between 5% and 35%. However, a large number of studies have found that it is difficult to achieve a good combination of strength and plasticity in single-phase FCC or BCC. Recently, a new type of high-entropy alloy, namely eutectic high-entropy alloy, has been proposed. The eutectic high-entropy alloy combines the advantages of traditional eutectic alloys and high-entropy alloys. It not only has good casting properties but also can avoid composition segregation. At the same time, due to its fine lamellar two-phase alternating structure, the eutectic high-entropy alloy has excellent strain hardening ability and is considered to have great potential in achieving the strength-plasticity balance of alloys.

[0003] In actual production, especially in the industrial production of large castings, the designed eutectic high-entropy alloys usually deviate from the eutectic composition. This deviation has an adverse effect on the mechanical properties of the eutectic high-entropy alloy, which is of great significance for industrial applications. The deviation of the eutectic composition has an important impact on the phase transformation and mechanical properties of the alloy. There is an urgent need for a high-performance eutectic high-entropy alloy with an adjustable composition range, especially for the industrial production of HEAs.

[0004] Studies have found that for high-entropy alloys of the Fe-Cr-Co-Ni-Al series, when their chemical composition is designed as Fe a Cr b Co c Ni d Al e , where a = 1, b = 1, c = 1, d = 2.1, e = 1, Fe-Cr-Co-Ni-Al is a eutectic high-entropy alloy, its yield strength is 540 MPa, tensile strength is 1100 MPa, and elongation at break is 18%, still not meeting the mechanical property requirements for strength-plasticity balance. Summary of the Invention

[0005] The problem existing in the prior art is that for Fe with a = 1, b = 1, c = 1, d = 2.1, e = 1 a Cr b Co c Ni d Al eEutectic high-entropy alloy, its mechanical properties still need to be further improved to meet the need of the strength-ductility trade-off. Aiming at the above technical problems, the present invention provides a Fe-Cr-Co-Ni-Al eutectic high-entropy alloy, and its chemical composition is designed according to atomic ratio and expressed as Fe a Cr b Co c Ni d Al e , where a = 49, 25 ≤ b ≤ 30, c = 9.8, 5 ≤ d ≤ 15, e = 2, and a + b + c + d + e = 100.

[0006] Preferably, the chemical composition is designed according to atomic ratio as Fe a Cr b Co c Ni d Al e , where a = 49, b = 27.4, c = 9.8, d = 11.8, e = 2.

[0007] Preferably, the chemical composition is designed according to atomic ratio as Fe a Cr b Co c Ni d Al e , where a = 49, b = 28.4, c = 9.8, d = 10.8, e = 2.

[0008] Preferably, the chemical composition is designed according to atomic ratio as Fe a Cr b Co c Ni d Al e , where a = 49, b = 29.4, c = 9.8, d = 9.8, e = 2.

[0009] Preferably, the purity of the metal raw materials used in the preparation process of the Fe-Cr-Co-Ni-Al eutectic high-entropy alloy is not less than 99.99%.

[0010] Preferably, the metal raw materials are in sheet or block form.

[0011] Preferably, the preparation method of the Fe-Cr-Co-Ni-Al eutectic high-entropy alloy includes the following steps:

[0012] (1) Using the simple substances of five metal elements, Fe, Cr, Co, Ni and Al, as raw materials, removing the oxides on the surface of the metal simple substances, then ultrasonically cleaning in alcohol for not less than 10 min, and then drying for standby;

[0013] (2) Convert the metal single-element raw materials obtained in step (1) into mass ratios according to the atomic ratio of the formula, and add them together into a vacuum melting furnace for vacuum melting under the atmosphere of a protective gas. After the melting is completed, the Fe-Cr-Co-Ni-Al eutectic high-entropy alloy is obtained.

[0014] Preferably, the vacuum degree of the vacuum melting is ≥5×10 -3 Pa.

[0015] Preferably, the protective gas is high-purity argon with a purity of ≥99.999%.

[0016] Preferably, the current for vacuum melting is 350 A, the single melting time is 3 min, and the melting is repeated 4 times. After each melting, the alloy ingot is turned over and the molten pool is electromagnetically stirred for 10 s.

[0017] The present invention has the following beneficial effects:

[0018] The present invention has found that for the Fe 49 Cr X Co 9.8 Ni 39.2-X Al₂ high-entropy alloy system, as the Cr / Ni molar ratio increases, the alloy undergoes a microstructural transformation from hypoeutectic to eutectic to hypereutectic. The Fe 49 Cr 28.4 Co 9.8 Ni 10.8 Al₂ obtained in the present invention is a eutectic high-entropy alloy with a yield strength of 612 MPa, a tensile strength of 823 MPa, and an elongation at break of 25.1%. The strength and plasticity of this alloy are well matched, solving the problem of poor strength and plasticity matching of existing high-entropy alloys. Moreover, the preparation method of the present invention is simple and reliable, and the selected elements are all non-toxic and easily accessible, with good safety and high economic value.

[0019] Description of the drawings:

[0020] Figure 1 : XRD diagrams of the high-entropy alloys obtained in Examples 1-3 and Comparative Example 1 respectively

[0021] Figure 2 : SEM diagrams of the high-entropy alloys obtained in Examples 1-3 and Comparative Example 1 respectively

[0022] Figure 3 : Mechanical property diagrams of the high-entropy alloys obtained in Examples 1-3 and Comparative Example 1 respectively

[0023] Figure 4 : Microhardness diagrams of the high-entropy alloys obtained in Examples 1-3 and Comparative Example 1 respectively Detailed implementation manners

[0024] The present invention will be described in detail below with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.

[0025] Example 1

[0026] The chemical composition of a Fe-Cr-Co-Ni-Al high entropy alloy is designed according to the atomic ratio: Fe a Cr b Co c Ni d Al e ; Among them, a = 49, b = 27.4, c = 9.8, d = 11.8, e = 2, that is, the high entropy alloy system is represented by Fe 49 Cr 27.4 Co 9.8 Ni 11.8 Al2, abbreviated as Cr-27.4. The specific preparation steps of Cr-27.4 are as follows:

[0027] (1) Using five metal elements of Fe, Cr, Co, Ni, and Al with a purity of not less than 99.99 wt% as raw materials, the metal elements were polished in sequence using 400# to 2000# sandpaper until there was no oxide on the surface, then ultrasonically cleaned in alcohol for 10 min, dried at 60°C for 1 h, and then used;

[0028] (2) The metal element raw material obtained in step (1) is prepared according to the Fe 49 Cr 27.4 Co 9.8 Ni 11.8 The atomic ratio of Al2 is converted into a mass ratio for proportioning and weighing, and the materials are placed in a non-consumable vacuum arc melting furnace, evacuated to 5×10-3Pa, and filled with high-purity argon (purity ≥99.999%) to 0.05MPa. The melting current is set to 350A, the single melting time is 3min, and the melting is repeated 4 times. After each melting, the alloy ingot is turned over and the molten pool is electromagnetically stirred for 10s. Then, the alloy melt is cast into a water-cooled copper mold with a size of 10×10×70mm to obtain a Fe-Cr-Co-Ni-Al high entropy alloy.

[0029] Example 2

[0030] The chemical composition of a Fe-Cr-Co-Ni-Al high entropy alloy is designed to be: a=49, b=28.4, c=9.8, d=10.8, e=2 according to the atomic ratio, that is, the high entropy alloy system is represented by Fe 49 Cr 28.4 Co 9.8 Ni 10.8 Al2, abbreviated as Cr-28.4. The specific preparation steps of Cr-28.4 are as follows:

[0031] (1) Using five metal elements of Fe, Cr, Co, Ni and Al with a purity of not less than 99.99 wt% as raw materials, polish them successively with 400# to 2000# sandpaper until there is no oxide on the surface of the metal elements. Then, ultrasonically clean them in alcohol for 10 min, dry them at 60 °C for 1 h, and set aside;

[0032] (2) Convert the atomic ratio of the spare metal element raw materials obtained in step (1) according to Fe 49 Cr 28.4 Co 9.8 Ni 10.8 Al₂ into a mass ratio for proportioning and weighing, and place it in a non-consumable vacuum arc melting furnace. Evacuate to 5×10 -3 Pa, fill it with high-purity argon gas (purity ≥ 99.999%) to 0.05 MPa, set the melting current to 350 A, the single melting time to 3 min, repeat melting 4 times, turn over the alloy ingot and electromagnetic stir the molten pool for 10 s after each melting, and then pour the alloy melt into a water-cooled copper mold with dimensions of 10×10×70 mm to obtain the Fe-Cr-Co-Ni-Al high-entropy alloy.

[0033] Example 3

[0034] The chemical composition of a Fe-Cr-Co-Ni-Al high-entropy alloy is designed according to the atomic ratio as: Fe a Cr b Co c Ni d Al e ; where a = 49, b = 29.4, c = 9.8, d = 9.8, e = 2, that is, the high-entropy alloy system is expressed as Fe 49 Cr 29.4 Co 9.8 Ni 9.8 Al₂, abbreviated as Cr-29.4. The specific preparation steps of Cr-29.4 are as follows:

[0035] (1) Using five metal elements of Fe, Cr, Co, Ni and Al with a purity of not less than 99.99 wt% as raw materials, polish them successively with 400# to 2000# sandpaper until there is no oxide on the surface of the metal elements. Then, ultrasonically clean them in alcohol for 10 min, dry them at 60 °C for 1 h, and set aside;

[0036] (2) Convert the atomic ratio of the spare metal element raw materials obtained in step (1) according to Fe 49 Cr 29.4 Co 9.8 Ni 9.8 Al₂ into a mass ratio for proportioning and weighing, and place it in a non-consumable vacuum arc melting furnace. Evacuate to 5×10-3 Pa, fill it with high-purity argon gas (purity ≥ 99.999%) to 0.05 MPa, set the melting current to 350 A, the single melting time to 3 min, repeat melting 4 times, turn over the alloy ingot and electromagnetic stir the molten pool for 10 s after each melting, and then pour the alloy melt into a water-cooled copper mold with dimensions of 10×10×70 mm to obtain the Fe-Cr-Co-Ni-Al high-entropy alloy.

[0037] Comparative Example 1 is the same as Example 2, except that the chemical composition of the Fe-Cr-Co-Ni-Al high-entropy alloy in Comparative Example 1 is designed according to the atomic ratio as: a = 1, b = 1, c = 1, d = 2.1, e = 1, that is, the high-entropy alloy system is expressed as Fe1Cr1Co1Ni 2.1 Al1, abbreviated as Cr-1.

[0038] Alloy Microstructure and Property Detection

[0039] I. Phase Analysis

[0040] Perform phase analysis on the high-entropy alloy systems obtained in Examples 1-3 and Comparative Example 1. Use the SMARTLAB X-ray diffractometer of Rigaku Corporation of Japan for phase analysis. The working voltage and current are 40 KV and 190 mA respectively, the scanning range is 20°-120°, and the scanning rate is 5° / min. The X-ray source is Cu Kα ray. The specific XRD results are as shown in the Figure 1 specification appendix. It can be found from the XRD results that all three alloys are duplex structures. As the content of Cr increases (while the content of Ni decreases), the intensity of the BCC peak of the alloy gradually increases, and the intensity of the FCC peak gradually decreases. Among them, the as-cast Cr-28.4 HEA contains an ordered BCC phase, that is, the B2 phase. The (100) superlattice diffraction peak is a typical peak of the B2 phase, similar to the intermetallic compound of NiAl. In Comparative Example 1, the AlCoCrFeNi 2.1 eutectic high-entropy alloy shows its FCC / B2 duplex structure.

[0041] II. Microstructure Characterization

[0042] Perform microstructure characterization on the high-entropy alloy systems obtained in Examples 1-3 and Comparative Example 1. The microstructure characterization uses a scanning electron microscope (SEM, FEI Quanta 250F). As shown in Figure 2 (a)-(b) of the specification appendix, Cr-27.4 HEAs show typical hypoeutectic microstructures, consisting of a light gray matrix structure and dark gray irregular dendritic structures, and the microstructure distribution is relatively uniform. As the content of Cr increases, the alloy changes from dendritic to a structure composed of a large number of interleaved lath side plate structures ( Figure 2(c)-(d)). Further increasing the Cr content, the Cr-29.4 HEAs form a typical hypereutectic structure and the lamellae become finer ( Figure 2 (e)-(f)). There is a transformation law of hypoeutectic-eutectic-hypereutectic in the alloy microstructure. Figure (g) shows the microstructure of the AlCoCrFeNi 2.1 eutectic high-entropy alloy in Comparative Example 1. This alloy exhibits a uniform and fine lamellar structure, with light gray being the FCC phase and dark gray being the BCC phase.

[0043] III. Uniaxial tensile mechanical property test

[0044] Quasi-static tensile mechanical property tests were carried out on the high-entropy alloy systems obtained in Examples 1-3 and Comparative Example 1. A servo universal material testing machine (TH-8201) was used for room temperature quasi-static tensile tests. The test specimens were made into dumbbell-shaped specimens according to the relevant regulations in the national standard of Metallic materials - Tensile testing at room temperature (GB / T 228.1-2010), and the strain rate was 2×10 -4 s -1 , as shown in the attached specification Figure 3 . As shown, when the Cr content of Cr-27.4 HEA was not regulated, it showed a low yield strength and excellent plasticity, that is, the yield strength was 408 MPa, the ultimate tensile strength was 656 MPa, and the fracture elongation was 26.6%. This high ductility is attributed to the high volume fraction of the soft FCC phase. With the increase of the Cr content, without sacrificing a large amount of plasticity, the strength of Cr-28.4 HEA was significantly improved. Its yield strength reached 612 MPa, the ultimate tensile strength was 823 MPa, and the fracture elongation was 25.1%. An excellent strength-plasticity balance was achieved and it showed the best comprehensive performance in this system. This is mainly attributed to the precipitation of the Cr-rich BCC phase. However, when the Cr content continued to increase, although the strength of Cr-29.4 HEA increased significantly, with the yield strength being 838 MPa and the ultimate tensile strength being 962 MPa, its plasticity decreased significantly, and the fracture elongation was only 14.2%. The reason is that the volume fraction of the BCC phase with high strength but poor plasticity is too large. In Comparative Example 1, the yield strength of the AlCoCrFeNi 2.1 eutectic high-entropy alloy was 540 MPa, the tensile strength was 1100 MPa, and the fracture elongation was 18%.

[0045] IV. Hardness property test

[0046] Hardness property tests were carried out on the high-entropy alloy systems obtained in Examples 1-3 and Comparative Example 1. Specifically, a hardness tester of model (Wilson VH1102) was used, with a force of 200 gf applied and a loading time of 15 s. The average value was obtained after 10 measurements on each sample. As shown in the attached specification Figure 4As shown, the hardness of Cr-27.4 HEA is only 210 HV. With the increase of Cr content and the decrease of Ni content, the hardness of Cr-28.4 HEA increases to 258 HV, which is mainly due to the precipitation of harder second phases in the alloy, resulting in an increase in hardness. With the further increase of Cr content, a large amount of hard and brittle second phases begin to precipitate, significantly increasing the hardness of the alloy, and the alloy hardness increases to 399 HV. In Comparative Example 1, the hardness of the AlCoCrFeNi 2.1 eutectic high-entropy alloy is 310 HV. In summary, Fe 49 Cr x Co 9.8 Ni 39.2-x The hardness of Al2 HEA increases with the increase of Cr concentration.

[0047] It can be seen from the above results that for the eutectic and near-eutectic Fe-Cr-Co-Ni-Al systems prepared by the present invention, with the increase of Cr content (simultaneously the decrease of Ni content), there is a transformation law of hypoeutectic-eutectic-hypereutectic in the alloy microstructure, the BCC content of the alloy increases, the FCC content decreases, the strength of the alloy increases, and the plasticity decreases. Among them, Fe 49 Cr 28.4 Co 9.8 Ni 10.8 The strength-ductility match of Al2 is better than that of the conventional AlCoCrFeNi 2.1 eutectic high-entropy alloy.

[0048] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy, characterized in that, The chemical composition is designed according to the atomic ratio and expressed as Fe a Cr b Co c Ni d Al e , where a = 49, 25 ≤ b ≤ 30, c = 9.8, 5 ≤ d ≤ 15, e = 2, and a + b + c + d + e = 100.

2. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 1, characterized in that, The chemical composition is designed by atomic ratio as Fe a Cr b Co c Ni d Al e , where a = 49, b = 27.4, c = 9.8, d = 11.8, e = 2.

3. The Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 1, wherein The chemical composition is designed by atomic ratio as Fe a Cr b Co c Ni d Al e , where a = 49, b = 28.4, c = 9.8, d = 10.8, e = 2.

4. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 1, characterized in that, The chemical composition is designed by atomic ratio as Fe a Cr b Co c Ni d Al e , where a = 49, b = 29.4, c = 9.8, d = 9.8, and e = 2.

5. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 1, characterized in that, The purity of the metal raw materials used in the preparation process of the Fe-Cr-Co-Ni-Al eutectic high-entropy alloy is not less than 99.99%.

6. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 5, characterized in that, The metal raw materials are in flake or block form.

7. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) Using the simple substances of five metal elements, Fe, Cr, Co, Ni, and Al, as raw materials, removing the oxides on the surface of the metal simple substances, then ultrasonically cleaning in alcohol for not less than 10 minutes, and then drying for standby; (2) Converting the metal simple substance raw materials obtained in step (1) into a mass ratio according to the atomic ratio of the formula, and adding them together to a vacuum melting furnace for vacuum melting under the atmosphere of a protective gas. After the melting is completed, the Fe-Cr-Co-Ni-Al eutectic high-entropy alloy is obtained.

8. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 7, characterized in that, The degree of vacuum in the vacuum melting is ≥ 5×10 -3 Pa.

9. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 7, characterized in that, The protective gas is high-purity argon with a purity ≥ 99.999%.

10. A Fe-Cr-Co-Ni-Al eutectic high-entropy alloy according to claim 7, characterized in that, The current for vacuum melting is 350 A, the single melting time is 3 minutes, and the melting is repeated 4 times. After each melting, the alloy ingot is flipped and the molten pool is electromagnetically stirred for 10 s.

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